The invention relates to the use of fluorinated ketones as wet cleaning agents for vapor reactors and vapor reactor parts.
The emission of global warming gases has received worldwide attention. The goal of the Kyoto Protocol, established at the United Nations Conference on Global Warming, was to lower emissions of carbon dioxide, methane, nitrous oxide, perfluorocarbon (PFC), hydrofluorocarbon (HFC), and SF6 to pre-1990 levels. Additionally, most manufacturers of semiconductors in the United States have signed a Memorandum of Understanding with the Environmental Protection Agency pledging to evaluate options for reducing PFC emissions.
Chemical vapor deposition chambers, physical vapor deposition chambers, and etching chambers are widely used in the semiconductor industry in connection with the manufacture of various electronic device and components. Such chambers use reactive gases or vapors to deposit, pattern, or remove various dielectric and metallic materials. Over time, undesirable deposits, typically fluoropolymers containing carbon, fluorine, hydrogen and oxygen atoms, inevitably build up on both the walls and parts of the chamber. These deposits are a source of potential contamination for the product being manufactured in the chamber and must be removed periodically. Perfluorocarbon gases such as C2F6 and C3F8 as well as perfluorinated nitrogen compounds such as NF3 have been used extensively for in situ plasma cleaning of the chamber. However, these gaseous materials are extremely stable compounds that contribute to global warming and are difficult to trap or treat with gas scrubbers.
The chamber walls and components can be cleaned using various liquid chemicals. The liquid cleaning agents currently used include water, various hydrocarbons such as acetone or isopropanol, and various fluorochemicals such as perfluorocarbons, hydrofluorocarbons, and hydrofluoro ethers. Water and hydrocarbons do not readily dissolve the fluoropolymer residue. Additionally, water requires long drying times and the hydrocarbons are flammable; these are both undesirable properties for a cleaning agent. Some fluorochemicals have the potential to contribute to global warming, another undesirable property for a cleaning agent.
This invention provides a method for removing deposits that build up on the walls and parts of a chemical vapor deposition chamber, a physical vapor deposition chamber, or an etching chamber using a liquid cleaning agent comprising a fluorinated ketone. The fluorinated ketones of this invention perform as well as the liquid perfluorochemicals traditionally used in the semiconductor industry but have lower global warming potential.
This invention provides a method of cleaning the walls and parts of a chemical vapor deposition chamber, a physical vapor deposition chamber, or an etching chamber using a liquid cleaning agent comprising a fluorinated ketone compound containing 5 to 10 carbon atoms. The cleaning agent can be a perfluoroketone, a compound in which all of the hydrogen atoms on the carbon backbone are replace with fluorine. Alternatively, the fluorinated ketone cleaning agent can have up to two hydrogen atoms and up to two non-fluorine halogen atoms including bromine, chlorine, and iodine attached to the carbon backbone. One or more heteroatoms can interrupt the carbon backbone of the molecule. The cleaning agent can also include an auxiliary halogenated compound that is miscible with the fluorinated ketone. Preferably, the auxiliary halogenated compound is a hydrofluoroether. The cleaning agent can be applied by wiping, spraying, soaking, and the like.
This invention provides a method of cleaning a chemical vapor deposition chamber, a physical vapor deposition chamber, or an etching chamber using a liquid cleaning agent comprising a fluorinated ketone compound having 5 to 10 carbon atoms, preferably 6 to 8 carbon atoms. The fluorinated ketones typically are liquids at room temperature with boiling points up to about 150xc2x0 C. Preferably, the fluorinated ketone is a perfluoroketone.
As used herein, the term xe2x80x9cvapor reactorxe2x80x9d includes chemical vapor deposition chambers, physical vapor deposition chambers, and etching chambers. Such chambers use reactive gases or vapors to deposit, pattern, or remove various dielectric and metallic materials. Vapor reactors are widely used in the semiconductor industry to manufacture a variety of electronic devices and components. Typically, gaseous perfluorocarbons such as CF4, C2F6, and C3F8 are used to etch various dielectric and metallic materials. The perfluorocarbons are usually mixed with oxygen gas and a radio frequency plasma is generated resulting in the formation of various radicals such as fluorine, carbon difluoride, carbon trifluoride, and the like. These radicals can undergo further reactions to form various fluoropolymers. The fluoropolymers deposit on the reactor walls and parts along with various other by-product of the manufacturing process. These by-products can include, for example, silicon-based residues and metallic residues such as tungsten, aluminum, and the like. Periodically, the vapor reactor needs to be cleaned to remove the fluoropolymers and other residues to avoid contaminating the product being prepared.
The traditional approach to removing the deposits has been to use various liquid cleaning agents. The liquid cleaning agents currently used include water, various hydrocarbons such as acetone or isoproponal, and various fluorochemicals such as perfluorocarbons, hydrofluorocarbons, and hydrofluoroethers. Water and hydrocarbons do not readily dissolve the fluoropolymer residue. Additionally, water requires long drying times and the hydrocarbons are flammable; these are both undesirable properties for a cleaning agent. The invention provides an alternative approach that avoids these undesirable properties in a manner that is more environmentally friendly than at least some prior approaches. The fluoropolymers and other residue that deposit on the reactor walls and parts can be dissolved using a liquid fluorinated ketone cleaning agent having 5 to 10 carbon atoms. The method of cleaning a vapor reactor can be used to partially or completely replace the conventional cleaning process with gaseous perfluorocarbons. As used herein, the term xe2x80x9ccleaningxe2x80x9d refers to removing the unwanted deposits that build up over time on the walls and parts of a vapor reactor.
The fluorinated ketones of the invention typically have a total of 5 to 10 carbon atoms and preferably have 6 to 8 carbon atoms. The cleaning agent can be a perfluoroketone, a compound in which all of the hydrogen atoms on the carbon backbone are replaced with fluorine. Alternatively, the fluorinated ketone cleaning agent can have up to two hydrogen atoms and up to two non-fluorine halogen atoms including bromine, chlorine, and iodine attached to the carbon backbone.
Representative examples of perfluorinated ketone compounds suitable as cleaning agents include CF3(CF2)5C(O)CF3, CF3C(O)CF(CF3)2, CF3CF2CF2C(O)CF2CF2CF3, CF3CF2C(O)CF(CF3)2, (CF3)2CFC(O)CF(CF3)2, (CF3)2CFCF2C(O)CF(CF3)2, (CF3)2CF(CF2)2C(O)CF(CF3)2, (CF3)2CF(CF2)3C(O)CF(CF3)2, CF3(CF2)2C(O)CF(CF3)2, CF3(CF2)3C(O)CF(CF3)2, CF3(CF2)4C(O)CF(CF3)2, CF3(CF2)5C(O)CF(CF3)2, CF3CF2C(O)CF2CF2CF3, perfluorocyclopentanone, and perfluorocyclohexanone.
Representative examples of fluorinated ketones with either one or two atoms other than fluorine attached to the carbon backbone include CHF2CF2C(O)CF(CF3)2, CF3C(O)CH2C(O)CF3,(CF3)2CFC(O)CF2Cl, CF2ClCF2C(O)CF(CF3)2, CF2Cl(CF2)2C(O)CF(CF3)2, CF2Cl(CF2)3C(O)CF(CF3)2, CF2Cl(CF2)4C(O)CF(CF3)2, CF2Cl(CF2)5C(O)CF(CF3)2, and CF2ClCF2C(O)CF2CF2CF3.
The fluoroketones can also contain one or more heteroatoms interupting the carbon backbone. Suitable heteroatoms include, for example, nitrogen, oxygen, and sulfur atoms. Representative compounds include, for example, CF3OCF2CF2C(O)CF(CF3)2 and CF3OCF2C(O)CF(CF3)2.
Fluoroketones can be prepared by known methods. One approach involves the dissociation of perfluorinated carboxylic acid esters of the formula RfCO2CF(Rfxe2x80x2)2 with a nucleophilic initiating agent as described in U.S. Pat. No. 5,466,877 (Moore). Rf and Rfxe2x80x2 are fluorine or a perfluoroalkyl group. The fluorinated carboxylic acid ester precursor can be derived from the corresponding fluorine-free or partially fluorinated hydrocarbon ester by direct fluorination with fluorine gas as described in U.S. Pat. No. 5,399,718 (Costello et al.).
Perfluorinated ketones that are alpha-branched to the carbonyl group can be prepared as described in U.S. Pat. No. 3,185,734 (Fawcett et al.). Hexafluoropropylene is added to acyl halides in an anhydrous environment in the presence of fluoride ion. Small amounts of hexafluoropropylene dimer and/or trimer impurities can be removed by distillation from the perfluoroketone. If the boiling points are too close for fractional distillation, the dimer and/or trimer impurity can be removed by oxidation with alkali metal permanganate in a suitable organic solvent such as acetone, acetic acid, or a mixture thereof. The oxidation reaction is typically carried out in a sealed reactor at ambient or elevated temperatures.
Linear perfluorinated ketones can be prepared by reacting a perfluorocarbon acid alkali metal salt with a perfluorocarbon acid fluoride as described in U.S. Pat. No. 4,136,121 (Martini et al.) Such ketones can also be prepared by reacting a perfluorocarboxylic acid salt with a perfluorinated acid anhydride in an aprotic solvent at elevated temperatures as described in U.S. Pat. No. 5,998,671 (Van Der Puy).
All the above-mentioned patents describing the preparation of fluoroketones are incorporated by reference in their entirety.
The fluorinated ketone cleaning agent can be applied alone, in combination with another fluorinated ketone, or in combination with one or more auxiliary cleaning agents that are miscible with the fluorinated ketone. The auxiliary cleaning agents are typically halogenated compounds including, for example, hydrofluorocarbons, hydrochlorofluorocarbons, perfluorocarbons, perfluoropolyethers, hydrofluoroethers, hydrofluoropolyethers, hydrochlorofluoroethers, fluorinated aromatic compounds, chlorofluorocarbons, bromofluorocarbons, bromochlorofluorocarbons, hydrobromocarbons, iodofluorocarbons, and hydrobromofluorocarbons. Representative examples of auxiliary cleaning agents include C5F11H, C6F13H, C4F9OCH3, C4F9OC2H5, C3F7CF(OC2H5)CF(CF3)2, CF3CH2CF2CH3, CF3CFHCFHCF2CF3, C6F14, C7F16, C8F18, (C4F9)3N, perfluoro-2-butyltetrahydrofuran, perfluoro-N-methylmorpholine, HCF2O(CF2O)n(CF2CF2O)mCF2H (where n is from 0 to 2, m is from 0 to 5, and the sum of n plus m is at least 1), C3F7I, benzotrifluoride, trans-1,2-dichloroethylene, and the like. Preferably, the auxiliary cleaning agent is a hydrofluoroether such as C4F9OCH3, C4F9OC2H5, C3F7CF(OC2H5)CF(CF3)2, and the like.
The fluorinated ketone cleaning agents can be applied by, for example, by wiping, spraying, and immersion of the parts for soaking or dipping. The cleaning agent can be combined with an inert propellant such as nitrogen, argon, or carbon dioxide to direct the cleaning agent to specific surfaces that need cleaning. The cleaning agent can be applied at either ambient or elevated temperatures, for example, up to 150xc2x0 C.
The perfluoroketones of the invention have much lower global warming potential (GWP) than the conventional perfluorocarbons used in the semiconductor industry. As used herein, xe2x80x9cGWPxe2x80x9d is a relative measure of the warming potential of a compound based on the structure of the compound. The GWP of a compound, as defined by the Intergovernmental Panel on Climate Change (IPCC) in 1990 and updated in 1998 (World Meteorological Organization, Scientific Assessment of Ozone Depletion: 1998, Global Ozone Research and Monitoring Projectxe2x80x94Report No. 44, Geneva, 1999), is calculated as the warming due to the release of 1 kilogram of a compound relative to the warming due to the release of 1 kilogram of CO2 over a specified integration time horizon (ITH):             GWP      x        ⁡          (              t        xe2x80x2            )        =                    ∫        0        ITH            ⁢                        F          x                ⁢                  C          Ox                ⁢                  ⅇ                                                    -                t                            /              τ                        ⁢                          xe2x80x83                        ⁢            x                          ⁢                  xe2x80x83                ⁢                  ⅆ          t                                    ∫        0        ITH            ⁢                        F                      C            ⁢                          xe2x80x83                        ⁢                          O              2                                      ⁢                              C                          C              ⁢                              xe2x80x83                            ⁢                              O                2                                              ⁡                      (            t            )                          ⁢                  xe2x80x83                ⁢                  ⅆ          t                    
where F is the radiative forcing per unit mass of a compound (the change in the flux of radiation through the atmosphere due to the IR absorbance of that compound), C is the atmospheric concentration of a compound, xcfx84 is the atmospheric lifetime of a compound, t is time and x is the compound of interest (i.e., C0x is the time 0 or initial concentration of compound x).
The commonly accepted ITH is 100 years representing a compromise between short term effects (20 years) and longer term effects (500 years or longer). The concentration of an organic compound in the atmosphere is assumed to follow pseudo first order kinetics (i.e., exponential decay). The concentration of CO2 over that same time interval incorporates a more complex model for the exchange and removal of CO2 from the atmosphere (the Bern carbon cycle model).
CF3CF2C(O)CF(CF3)2 has an atmospheric lifetime of approximately 5 days based on photolysis studies at 300 nm. Other perfluoroketones show similar absorbances and thus are expected to have similar atmospheric lifetimes. A measured IR cross-section was used to calculate the radiative forcing value for CF3CF2C(O)CF(CF3)2 using the method of Pinnock, et al. (J. Geophys. Res., 100, 23227, 1995). Using this radiative forcing value and the 5 day atmospheric lifetime, the GWP (100 year ITH) for a perfluoroketone with 6 carbon atoms is 1 while the GWP for C2F6 is 11,400. The perfluoroketones of the invention typically have a GWP less than about 10. As a result of their rapid degradation in the lower atmosphere, the perfluorinated ketones have short lifetimes and would not be expected to contribute significantly to global warming.
Additionally, the fluorinated ketones have low toxicity. For example, the perfluoroketone CF3CF2C(O)CF(CF3)2 has low acute toxicity based on short-term inhalation tests with rats. Based on a four-hour exposure period, the LC50 concentration is 100,000-ppm perfluoroketone in air. This toxicity is comparable to that of the perfluorocarbons presently used as cleaning agents in the semiconductor industry.
The following examples further describe the methods of using fluorinated ketones as cleaning agents. The examples are provided for exemplary purposes to facilitate understanding of the invention and should not be construed to limit the invention to the examples. Unless otherwise specified, all percentages and proportions are by weight.